Channel 4’s sci-fi thriller Humans has become the broadcaster’s biggest original drama hit since the Camomile Lawn more than 20 years ago.

The £12 million fantasy series, which stars William Hurt, Gemma Chan, Katherine Parkinson and The Thick Of It’s Rebecca Front, had a consolidated audience of 6.1 million viewers, a 23% share of the audience, for its opening episode.

Humans: a bankable British TV show that isn't a costume drama

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You have to go back to 1992 – a pre-digital age when most homes had only four channels in the UK – to the last time an originated Channel 4 drama had a bigger audience.

A co-production with US broadcaster AMC, maker of Mad Men and Breaking Bad, Humans explores the blurring of the lines between humans and machines, so-called domestic “Synths”.

Executive producer Derek Wax said the drama had proved popular because it “deals with universal themes. It never felt like science fiction to me, it felt like a story exploring what it means to be human”.

Wax said: “A lot of science fiction takes place in a hugely futuristic landscape and we wanted it to be in a parallel present with just one twist. Instead of a nightmare vision where robots were taking over, we wanted the jury to be out, for the audience to be torn.”

Torn, that is, between the “attractions of having someone in the house who can do all the menial functions and make our life easier, and the costs and implications that may come with that”.

Wax said: “The scenario feels very prescient. We live in a world where we are more and more dependent on technology from the phones we check every five minutes to the automated machines we deal with every day.”

Made by Kudos, producer of Broadchurch and Life on Mars, Humans was written by Spooks writers Sam Vincent and Jonathan Brackley based on a Swedish TV series, Real Humans.

Hollywood star Hurt is no stranger to some of the issues tackled by the series, having previously starred in Steven Spielberg’s 2001 film exploring sentient machines in A.I. Artificial Intelligence.

The drama has not yet been recommissioned for a second series but its ratings performance suggests its return is likely.

The Channel 4 series began with an overnight audience of just over 4 million viewers two weeks ago. The consolidated audience includes people who recorded it and watched it over the subsequent seven days.

The overnight audience for the second episode on Sunday dropped, although not markedly by current standards, by around 20% to 3.2 million viewers.

Humans had more than twice the overnight audience of BBC1’s Jonathan Strange & Mr Norell, which was on at the same time and was watched by just 1.6 million viewers, a third of its launch audience five weeks ago.

It brings an end to BBC1’s successful Sunday night drama run, a slot previously occupied by its big-rating Poldark and JK Rowling adaptation, A Casual Vacancy.

Piers Wenger, head of drama at Channel 4, said: “It asks questions of the contemporary world like all good drama should but Humans never fails to be entertaining as well. It’s a thrilling ride.”

Channel 4 has had several acclaimed dramas in recent months and two which began with overnight audiences of around 3 million or more.